Benefits of the New Reference Frames Dru Smith Joe Evjen 60 minutes April 13, 20152015 Geospatial Summit1

Benefits of the New Benefits of the New Reference FramesReference Frames

Dru SmithDru SmithJoe EvjenJoe Evjen

60 minutes60 minutes

April 13, 2015 2015 Geospatial Summit 1

Outline• Needed repairs

• Benefits of new frames:– Repairs– Improvements


What is a repair?• A fix to something in the current

system that is currently causing NGS to:– Fail to provide heights, or– Provide inaccurate heights, or– Put undue burden on users, or–Waste resources


What is an improvement?• A change to something in the current

system that by itself is not causing significant problems, but whose cost/benefit ratio is worthwhile and which helps NGS to provide:– Better service and/or– Better accuracy and/or– Better sustainability and/or– Better efficiency


Needed Repairs


Needed Repairs: NAVD 88• Inherent weaknesses of passive marks– Fragility, convenience, movement– Cost-prohibitive maintenance

• Adjustment issues–Minimally constrained, Helmert

approximation, inconsistent surface gravity surveys

• Sparseness• Bias and Tilt–WRT GRACE/GOCE geoid models


Needed Repairs: NAD 83• NAD83 frame ≠ GPS navigation frame• NAD83 frame ≠ WAAS navigation frame• NAD83 frame ≠ satellite orbits frame• NAD83 frame ≠ satellite product frame• NAD83 frame ≠ international geodetic

frame– International flights take off & land on different

datums– Many geodetic tools assume ITRF as default


map how you navigate?

1.3

2.5

3.8

5.06.3 meters

Your GNSS frame, ITRFYour GNSS frame, ITRF

As GNSS un-augmented user range error improves over time …

NAD 83(2011) to NAD 83(2011) to IGS08 at epoch 2022.0IGS08 at epoch 2022.0

NAD 83(2011) to NAD 83(2011) to IGS08 at epoch 2022.0IGS08 at epoch 2022.0

NAD 83(PA11) to NAD 83(PA11) to IGS08 at epoch 2022.0IGS08 at epoch 2022.0

Needed Repairs: Island datums

(PRVD02, ASVD02, NMVD03, GUVD04, VIVD09)


• Many of the same issues as NAVD 88– Fragility, convenience, movement, MCA,

sparseness, bias, tilt

• Normal orthometric heights

Needed Repairs: Hawaii


• No vertical datum exists!

Needed Repairs: IGLD 85• Many of the same issues as NAVD 88– They were co-defined from the same

leveling and gravity data

• Thirty years of GIA have changed the levels of the lakes


Repairs that come with the new

reference frames


Repairing NAVD 88


Repairing NAVD 88*Problem: Fragility of bench marks

Repair: In the new geopotential reference frame, orthometric heights are available to GNSS receivers without need for any bench marks


* and PRVD02, ASVD02, NMVD03, GUVD04, VIVD09

Repairing NAVD 88*Problem: Inconvenient bench mark locations

Repair: In the new geopotential reference frame, orthometric heights are equally available to GNSS receivers everywhere in the USA



Repairing NAVD 88*Problem: Unchecked movement of bench marks

Repair: In the new geopotential reference frame, orthometric heights at the epoch of the survey, are available to GNSS receivers because of time-dependent geoid models and time-dependent CORS positions



Repairing NAVD 88*Problem: Minimally Constrained Adjustment (absolute accuracy of heights is dependent on distance from origin)

Repair: In the new geopotential reference frame, the absolute accuracy of orthometric heights will have greater consistency throughout the country.



Repairing NAVD 88Problem: Helmert Approximation (heights rely on a first-order approximation which doesn’t propagate into accuracy statistics)

Repair: In the new geopotential reference frame, approximations are being quantified and bounded and will be reflected in accuracy statistics.


Repairing NAVD 88Problem: Inconsistent surface gravity surveys (heights rely 2 million surface gravity measurements which span decades and reflect no time dependency)

Repair: In the new geopotential reference frame, the gravity field will be consistent, and epoch dependent, directly influencing the time dependent geoid and time dependent orthometric heights


Repairing NAVD 88*Problem: Sparseness (bench mark spatial distribution tends to cluster around population clusters)

Repair: In the new geopotential reference frame, orthometric heights are equally available to GNSS receivers everywhere in the USA



Benefits of repairs: NAVD 88*

Problem: Bias and Tilt (“zero height surface” of datum is not the geoid)

Repair: In the new geopotential reference frame, the geoid will be the zero height surface, and will be built upon global satellite models



Repairing NAD 83


Repairing NAD 831)Align US frame with ITRF, GPS, WAAS2)Remove non-geocentricity3)Move beyond cascade of NAD83 realizations4)Better agreement across USA – Mexico border5)Velocities everywhere, so weuse similar techniques everywhere


Repairing Island datums (PRVD02, ASVD02, NMVD03, GUVD04,

VIVD09)


Repairing Island datums(PRVD02, ASVD02, NMVD03, GUVD04,

VIVD09)

Problem: Normal Orthometric Heights (heights do not rely on actual gravity measurements)

Repair: In the new geopotential reference frame, orthometric heights will be available to GNSS receivers, not normal orthometric heights


Repairing Hawaii


Repairing Hawaii

Problem: No Vertical Datum (NGS has never officially defined a vertical datum for Hawaii)

Repair: In the new geopotential reference frame, orthometric heights will be available to GNSS receivers in Hawaii, consistent with heights across the North American continent


Repairing IGLD 85


Repairing IGLD 85

Problem: GIA changes aren’t reflected in IGLD 85

Repair: In the new geopotential reference frame, dynamic heights at the epoch of the survey, are available to GNSS receivers because of time-dependent geoid models, time-dependent CORS positions and time dependent gravity field models


Improvements that come with the new reference frames


Improving Heights

Continental consistency

In the new geopotential reference frame, heights will be consistent from pole to equator and Aleutians to Greenland.


Extent of 2022 geoid model used for new geopotentialreference frame


Hawaii

Many US Pacific Territories(not Guam, CNMI nor American Samoa)



CanadaAlaska, includingentire Aleutian Island Chain

CONUS (USA)

Mexico

All Central American Countries

All Caribbean Countries

Bermuda


Improving Heights

Time-dependent heights on passive control

In the new geopotential reference frame, heights on passive control will eventually be stored at and distributed by NGS, and changes over time will be reflected as actual changes


1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030

2.000

2.050

2.100

2.150

2.200

2.250

2.300

2.350

H

time

Assume “H” was determined four different times:1990: 2.1001994: 2.1102002: 2.1902009: 2.180

1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030

2.000

2.050

2.100

2.150

2.200

2.250

2.300

2.350

H

time

In standard NGS procedure, a height is held fixed untilreplaced. So plotting the height as seen on a datasheetover time would look like this:

Height unknown before first survey

1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030

2.000

2.050

2.100

2.150

2.200

2.250

2.300

2.350

H

time

This will change in the future. First, error bars will be shown.Shown here are the same values of “H”, but with error bars representing their standard deviations.

1990: 2.100 +/- 0.0375 (3.75 cm)1994: 2.110 +/- 0.0250 (2.50 cm)2002: 2.190 +/- 0.0200 (2.00 cm)2009: 2.180 +/- 0.0250 (2.50 cm)

1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030

2.000

2.050

2.100

2.150

2.200

2.250

2.300

2.350

H

time

Using least squares, we could fit a line, usingappropriate weights to fit to the data

1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030

2.000

2.050

2.100

2.150

2.200

2.250

2.300

2.350

H

time

Using a simple H = mt+b fitting, we get:

m = 0.00505 m/y (+5.05 cm uplift per year)b(1970) = 2.004 m

H = (0.00505)(t

-1970) + 2.004

1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030

2.000

2.050

2.100

2.150

2.200

2.250

2.300

2.350

H

time

Now, we can find H at various time intervals.

1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030

2.000

2.050

2.100

2.150

2.200

2.250

2.300

2.350

H

time

And propagating the actual measurement error forwardand backward in time, we see that there is a strong dependence on higher accuracy height estimates occurring near the actual surveys.

1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030

2.000

2.050

2.100

2.150

2.200

2.250

2.300

2.350

H

time

Compare this with current NGS procedures…

Height unknown before first survey

1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 2025 2030

2.000

2.050

2.100

2.150

2.200

2.250

2.300

2.350

H

time

Compare this with current NGS procedures…

The only place current NGS procedures match the predicted heights

5 cm

10 cm*

(*andgrowing)

Improving Dynamic Heights

In the new geopotential reference frame, dynamic heights will be available from GNSS surveys, rather than just leveling surveys


Improving Clarity

“All coordinates are referenced to the North American Datum of 1983 (NAD 83) which is equivalent to the World Geodetic System 1984 (WGS 84)”

- U.S. Supreme Court, Dec 15, 2014

In the new geopotential reference frame, the name “NAD 83” will be gone, and issues such as this will hopefully be left behind as well.


Thank You!


http://www.ngs.noaa.gov/datums/newdatums/

Extra Slides




Needed Repairs: IGSN 71Most NGS surface gravity is in IGSN 71, an international network, not under NGS control

•Based on pre-microGal absolute meters

•No maintenance


Documents

Benefits of the New Reference Frames Dru Smith Joe Evjen 60 minutes April 13, 20152015 Geospatial Summit1